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Currently when removing an ipmi_user the removal is deferred as a work on the system's workqueue. Although this guarantees the free operation will occur in non atomic context, it can race with the ipmi_msghandler module removal (see [1]) . In case a remove_user work is scheduled for removal and shortly after ipmi_msghandler module is removed we can end up in a situation where the module is removed fist and when the work is executed the system crashes with : BUG: unable to handle page fault for address: ffffffffc05c3450 PF: supervisor instruction fetch in kernel mode PF: error_code(0x0010) - not-present page because the pages of the module are gone. In cleanup_ipmi() there is no easy way to detect if there are any pending works to flush them before removing the module. This patch creates a separate workqueue and schedules the remove_work works on it. When removing the module the workqueue is drained when destroyed to avoid the race. [1] https://bugs.launchpad.net/bugs/1950666 Cc: stable@vger.kernel.org # 5.1 Fixes: 3b9a907223d7 (ipmi: fix sleep-in-atomic in free_user at cleanup SRCU user->release_barrier) Signed-off-by: Ioanna Alifieraki <ioanna-maria.alifieraki@canonical.com> Message-Id: <20211115131645.25116-1-ioanna-maria.alifieraki@canonical.com> Signed-off-by: Corey Minyard <cminyard@mvista.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.